This invention relates to a testing apparatus and more particularly to a pointing bar fatigue testing apparatus for fatigue destruction test upon pointing bars used in input devices.
The pointing bar input means are widely used in various types of input devices such as control panels, keyboards, remote control devices and the like. The pointing bar input means can also be seen in some other type of the electronic devices such as mouses, joy sticks, touch pads, track balls, pointing sticks and the like. The basic design of pointing bar structure is to produce analog signals resulting from strain caused by a force applying on the pointing bar at a selected direction. The analog signals are output for further computer use. For instance, a pointing bar may be installed between any two adjacent keys in a keyboard of a notebook computer, and a corresponding strain can be produced by a force applied to the top of the pointing bar.
By means of design and arrangement, the strain incurred in the pointing bar may be converted into respective output signals that may be used as movement reference of the computer cursor.
Regarding the production of the pointing bars, especially the strut-type bars, fatigue strength is an important indicator of the production quality. Thus, sampling fatigue strength test is one of the test items during the manufacturing process of the pointing bars.
Generally, it is known that when material is subjected to a force or stress greater than its tensile strength, the material may result in instant fracture. On the other hand, if the stress is smaller than the tensile strength, repeating stress can also lead to a crack in the material, which may grow and result in final fracture after a period of time. As well known in the art, 90% of the material fracture are amounted to fatigue, either static or dynamic. In the case that the repeating stress is dynamic in nature, the resulted fracture is called a dynamic fatigue fracture. In the case that the repeating stress is static in nature, the fracture is called a static fatigue
Because the pointing bar is short and brittle (usually made of ceramics), a conventional fatigue testing apparatus cannot be applied. Thus, special testing apparatus are usually needed to carry out the testing of the pointing bar. In U.S. Pat. No. 5,544,530, Rudisill et al disclosed one of the special apparatus for fatigue testing of the pointing bars.
FIG. 1 illustrates a schematic view of the testing apparatus taught by Rudisill et al. As shown, the apparatus has a motor with which a spindle 13 can rotate. The spindle 13 further contacts forcedly and eccentrically with an elastic arm 15 via a round disk 17 at one end thereof so that the elastic arm 17 can be slightly bent in the middle portion. The bending force applied to the disk 17 can thus be transmitted to pointing bar 11 axially engaged with the center of the disk 17. When the motor is actuated, the rotating spindle 13 will drive the elastic arm 15 running around the disk 17 and consequently applying moving bending stress upon the pointing bar 11 to mimic radial and repeating forces upon the pointing bar.
However the prior art set forth above has the following shortcomings:
1. The elastic arm makes the motor rotation not even, nor stable. It can only be used for low speed testing. Therefore, the test scope and result are limited and time-consumed.
2. It does not take into account the centrifugal force resulting from the rotating elastic arm. The force assigned to the pointing bar is not equal to the actual force received by the pointing bar, and thus the testing result cannot tell a true story.
3. As the elastic arm is horizontally positioned, the effect of gravitational force should be included. Upon including the gravitational force, the resultant force upon the pointing bar is the greatest when the elastic arm moves to the highest portion of the disk 17 and is the lowest when it moves to the lowest portion of the disk 17.
Hence, there is still a need for developing a pointing bar fatigue testing apparatus that can reduce the effect of the gravitational force and the centrifugal force and may perform the test speedily without sacrificing the system stability.
In view of aforesaid disadvantages, this innovation aims at providing a pointing bar fatigue testing apparatus that has a horizontal rotating disk for holding the pointing bar vertically to free the effect of gravitational force, so that the problems resulting from not evenly and not accurately applying force may be resolved.
It is an object of this invention to provide a pointing bar fatigue testing apparatus that is characterized on simple structured, evenly force applying, no gravitational force impact, and accurate performance.
The pointing bar fatigue testing apparatus of this invention may perform fatigue test for different shapes of pointing bar. It mainly includes a power source, a force feeding means and an pointing bar seat. The power source may be a motor having an extending spindle.
The force feeding means has a flat board, a slide bar and a motor spindle. The flat board has two spaced border flanges which have respective round openings therein for holding the slide bar. The slide bar has a bore in the middle. There is a spring engaging with one end of the slide bar and exerting spring force on the bore.
The pointing bar seat is preferably a modular member located above the force feeding means.
When in use, one end of the pointing bar is fixed to the pointing bar seat and another end engages with the bore in the slide bar. When the power source rotates the force feeding means, the spring exerts force on the pointing bar located through the bore for performing fatigue testing upon the pointing bar.
In an embodiment of this invention, there is a sensor means located below the power source for sensing the rotation speed of the power source disk plate. A controller may be included to wire with the sensor means for indicating and controlling the power source rotation speed.
In another embodiment of this invention, the power source may include a reducer which may be a gear set, a friction wheel set, a belt pulley set and the like. The gear set may be a combination of a large gear and a small gear for reducing rotation speed from the power source to the force feeding means.
In yet another embodiment of this invention, the slide bar may include a bearing located in the middle thereof. An inner ring of the bearing can form a force transmission point to the pointing bar.
In a still another embodiment, the force feeding means may include at least one side wall for supporting at least one side of the force feeding means. It is preferably to have two side walls for supporting two sides of the force feeding means. The side wall may slidably engage with the force feeding means to adjust the position of the force feeding means.